link May 21 Meeting Notes
(by Erik Arvidsson)
John Neumann (JN), Allen Wirfs-Brock (AWB), Eric Ferraiuolo (EF), Erik Arvidsson (EA), Luke Hoban (LH), Doug Crockford (DC), Yehuda Katz (YK), Brendan Eich (BE), Sam Tobin-Hochstadt (STH), Alex Russell (AR), Dave Herman (DH) (calling in), Bernd Mathiske (BM), Andreas Rossberg (ARB), Mark Miller (MM), Tom Van Cutsem (TVC), Jasvir Naga (JNA), Istvan Sebestyen (IS)
JN: Going through the agenda Adding proto Unifying iterator/generator APIs Talking about getting user stats for test-262... YK: Prioritize ES6 items. So that we don't get do ES7+ items before
Minutes approved unanimously
link 4.1 Object.freeze
DC: Today Object.freeze throws when primitives are passed in. Suggesting not throwing when a value type is passed in.
MM: Object.isExtensible would return false for primitives
EA: This would give an inconstint view for primitives.
AWB/YK: (In strict mode) numbers and strings lazily box so the assignment never fails.
MM: Proxies are allowed to be non extensible and throw away.
ARB: Is the suggestion to lazily wrap primitives?
MM: No, then
Object.isExtensible(7) would return true because the wrapper is
AWB: In most of the new changes we are not doing unnecessary coercion.
YK: The Chrome dev tools,
console.dir(7), says "no properties" which
supports treating these as empty objects.
MM: The only observable wrapper is the
this wrapper in non strict mode.
AWB: In the new spec,
MM: Agrees violently!
- DC+AWB to work out the details
link 4.2 WeakSet
Do we need them?
MM: Trivial shim around WeakMap.
YK: Often wanted it
AWB: Adds no new capabilities.
AR: We should not limit ourselves to what is a new primitive capabilities
AI(AWB): add to spec
- Add WeakSet in ES6
link 4.4 Proxies
TVC's presentation on Notification Proxies: https://docs.google.com/file/d/0B9iYRsLxmdqUd1RsdHZtazliWmc/edit?usp=sharing
- shifts the burden from spec writers/implementors to users (need to use shadow target even for non-frozen objects)
- implementors will deal with spec bugs related to invariant violations as they come up
- Notification proxies are not approved.
- MM & TVC are still happy with direct proxies.
link Proxy Invoke Trap and wrong |this|-binding on built-in methods
AWB: with current default behavior of "get", "Caretaker" will break on built-ins such as Date, because the |this| binding is by default set to the proxy, so the Date built-in method will not find the correct private state.
ARB: Same issue with binary methods
STH: We should add invoke trap but not change the object model
MM: Pleasant to have. Separate from private state.
AWB: used to think this was an issue with proxies, but convinced that it's an API issue: we need to provide default handlers that do the right thing, and which users can subclass. In particular, want a handler that, on forwarding, rebinds |this| to the target.
STH: If you want to proxy a Date method the underlying
this needs to be a non wrapped Date object.
TVC: previously proposed a Handler API that defines derived traps and fundamental traps, allows you to subclass and inherit correct behavior for derived traps. Can be used as the basis.
AWB/TVC: invoke trap would make it easier to control |this|-binding
DH: Never liked breaking the semantics of [[Get]] + [[Call]]
TVC: there already exist invoke-only properties on platforms with
AWB: For a [[Call]] it might be important to control
this but by the time the [[Call]] is happening you do not know what
this to use.
DH: ActionScript has a proxy and they do have an invoke trap.
BM: The most common action is to invoke a method.
? : we already gave up on the |this| invariant for accessors: in ES5, if obj.x is a getter, |this| will always be bound to obj in the getter. With proxies this is no longer true.
AI(AWB, TVC): Add spec for invoke. Tom and Allen to work out details of a Handler API that accommodates both "caretaker" (aka forwarding) and "virtual object" use cases.
- Add invoke trap.
MM: Everybody in this room wants classes and want to post pone private state to after ES6
ARB: Based on feedback, people do not want unique symbols, only private symbols.
MM: Private symbols do not work with proxies.
TVC: can still use WeakMap for private state.
DH: The most common cases where true information hiding is self hosting. The stakes are too high for the browser engines.
YK: If "iterator" would be a private symbol, you cannot create a proxy that will work with for-of loops.
ARB: Symbols (unique and private) and relations overlap.
BE: If we add symbols now we are stuck with them.
LH: Future users will be confused. They will not know what to use
BE: Unique symbol is very different from class private syntax.
AWB/MM: If we first did relationships we might not need symbols.
MM: Relationship published but not reflective.
MM: Difference between relationships and symbols: where is the mutability? This forces us to have both relationships and unique symbols.
link 4.13 Endianness of Typed array
ARB: Remember it as if we should specify this.
BE: Endianness in Typed Arrays is unspecified.
DH: Keep it open for now... Same system to same system. Using data view, which is explicit, there is no problem.
STH: We don't know what WiiU will do?
AWB: Or they decide not to comply to the spec
DH: WebGL is endian agnostic.
- Leaving it unspecified in ES6.
link 4.18 proto
STH: Recollection, first as data property, then as an accessor. Then discussed the power of that setter. Set the [[Prototype]] in the [[Realm]]. Then Allen wrote the spec. Realized that there were some problems with that design. Roughly the same power as
MM: Existence of a setter... as long as we have the extensibility restriction, that is sufficient.
AWB: Why restrict
__proto__ and not other
DH: Objects belonging to a realm is a bad idea.
MM: No more reason to restrict the setter.
__proto__ setter to the object upon extraction
MM: In SES objects that are non extensible. Not going to remove
__proto__ going forward.
Object.prototype.__proto__ is a data property, making it non writable prevents other objects to use assign to set
Object.prototype.__proto__ is an accessor that just calls
AR: Best practice on the web is important even in the future.
TVC: If we have
Object.prototype.__proto__ do we want
Object.setPrototypeOf or just
AWB: Makes sense to have
Object.setPrototypeOf for consistency.
EA: Where do we draw the line (
DH: People will need to be able to get this before we have a reflect module.
TVC: We need both because they have different return value (
Reflect.setPrototypeOf returns boolean success value).
__proto__is an accessor on
- The setter mutates [[Prototype]].
- There is no "poison pill".
link Naming of @@iterator
AWB: Suffix with $
STH: Opposed to special naming. People don't do this kind of naming convention. Why do we want to introduce this concept?
- No special naming
link Generators and iterators
send is gone in favor of
next(arg) (only first arg is passed through in
YK: Whether generators return a frozen object or not?
close is gone